调用的接口：

https://api.mch.weixin.qq.com/v3/refund/domestic/refunds

入参：

{
    "amount": {
        "currency": "CNY",
        "refund": 18000,
        "total": 18000
    },
    "out_refund_no": "SS1729156829593831RF",
    "out_trade_no": "SS1729156829593831",
    "reason": "主动申请退款"
}

响应：

{
    "code": "RESOURCE_NOT_EXISTS",
    "message": "订单不存在"
}